In 1940 photographer Gjon Milli attached lights to the boots of ice skaters and photographed their routines with a long shutter speed. Nine years later, while on assignment from Life Magazine to photograph Picasso, Milli showed him the ice skater photos. Picasso was so taken with idea that he immediately grabbed a light pen, and the two men created a series of their own.
{via Kathy Akey and Light Painting Photography}
